Method of manufacturing a turbine wheel having inserted blades, and a wheel obtained by performing the method

ABSTRACT

To manufacture a turbine wheel having blades made of a ceramic or composite material and inserted into a metal hub, firstly blades (16) are manufactured that are right cylindrical, each blade having a base (18) through which a hole is formed; a cylindrical ring (20) is formed, the ring being provided with orifices through which the bases (18) of the respective blades (16) are inserted; the blade bases (18) are successively threaded onto an open annular rigid metal wire (30); the resulting assembly (16, 20, 30) is disposed inside a sealed housing (161); hot isostatic compaction is performed so as to compact a metal alloy in powder form (41) inside the sealed housing (161) so as to make the hub of the turbine wheel (100) while embedding the blade bases (18) and the metal wire (30) by using the powder metallurgy technique; and the outside portion of the sealed housing (161) delimiting the hub of the turbine wheel (101) is machined. Application, in particular, to the field of aeronautical or space engineering.

FIELD OF THE INVENTION

The present invention relates to a method of manufacturing a hybridturbine wheel having blades made of a ceramic or composite material andfixed on a metal hub, and also to an inserted-blade turbine wheelobtained by performing the method. The invention is applicable both tothe field of industry, and to the field of aeronautical and spaceengineering.

PRIOR ART

Documents EP-A-0 176 386, FR-A-2 637 319, and FR-A-2 476 766 discloseexamples of one-piece turbine wheels in which both the hubs and theblades are made entirely of composite materials. Such turbine wheelsoffer the advantage of being lightweight, but they are difficult tomanufacture because the unidirectional strength characteristics of thecomposite fibers must be adapted to the multidirectional stress fieldthat exists in an assembly constituted by a disk and by blades, andbalancing problems also exist.

In that type of turbine wheel, it is also necessary to take into accountthe shear and deformation characteristics of the matrix and of thefibers, and there is also a danger that the blades might shear off atthe rim.

Also, Documents FR-A-2 608 674, EP-A-0 367 958 and U.S. Pat. No.4,326,835 disclose examples of compound turbines having blades made of aceramic or composite material, each of the blades having a base enablingit to be inserted into a metal hub.

In that type of turbine, the blades are manufactured in the form ofdiscrete components, and they are then received and locked in theperiphery of a metal disk by assembly means, e.g. dovetail means.

Such a blade has a complicated shape because its base is dovetail orChristmas tree shaped. Therefore, it is difficult to machine thecomposite material, and also to assemble the blades with the hub.

Turbine rotors that are made entirely of metal are also known. But theyhave considerable mass, and, as a result of the way in which they areassembled, their speeds of rotation are limited.

OBJECT AND BRIEF DESCRIPTION OF THE INVENTION

An object of the present invention is to remedy the above-mentioneddrawbacks of known turbine wheels, and in particular to enable turbinewheels to be manufactured simply that have improved mechanical strengthand that are capable of withstanding high speeds of rotation underdifficult environmental conditions.

To these ends, the invention provides a method of manufacturing aturbine wheel having blades made of a ceramic or composite material andinserted into a metal hub, said method being characterized in that itcomprises the following steps:

a) the blades are manufactured from a ceramic or composite material,each blade having an essentially right cylindrical shape with across-section defining a predetermined non-circular shape, and a hole isformed in the base of each blade, the hole being essentiallyperpendicular to the axis of the blade;

b) a closed cylindrical ring is formed of predetermined height thatcorresponds to the width of the hub of the wheel, the ring beingprovided with orifices corresponding to the predeterminedcross-sectional shape of the blades;

c) the bases of the blades are inserted through said orifices in therim-forming cylindrical ring;

d) the bases of the various blades inserted through the cylindrical ringare successively threaded onto an open annular rigid metal wire whichhas a smaller diameter than the cylindrical ring and which passesthrough said holes formed in the bases of the blades;

e) the assembly constituted by the blades, by the cylindrical ring andby the annular rigid metal wire is disposed inside a sealed housingafter removable spacers or inserts have been interposed between theheads of the blades projecting radially outwards beyond said cylindricalring;

f) hot isostatic compaction is performed so as to compact a metal alloyin powder form that is inserted into the sealed housing so as to makethe hub of the turbine wheel while embedding the blade bases and theannular rigid metal wire by using the powder metallurgy technique; and

g) the outside portion of the sealed housing delimiting the hub of theturbine wheel is machined and said removable spacers are removed.

By retaining the blades by means of the rigid metal wire passing throughtheir bases, it is possible to hold the blades effectively both whilethey are being installed, and during the final assembling step in whichthe blade bases and the rigid metal wire are embedded in the hub made ofa metal alloy by hot isostatic compaction.

The method of the invention enables blades to be manufactured "by theyard". According to a particular characteristic of the presentinvention, a long cylindrical length of ceramic or composite material ismanufactured in a single operation, said length having a cross-sectionof predetermined uniform shape, and then said long length of ceramic orcomposite material is cut up into individual blades.

By using a "sausage-making" technique, manufacturing the blades isgreatly simplified compared with blades made of a composite material andhaving complex shapes, with bases that are dovetail or Christmas treeshaped.

The method of the invention increases the mechanical strength of thewheel, which is a compound wheel, in which the blades made of acomposite material offer good resistance to creep, to oxidation, and tovibrations, in a high-temperature environment, and the metal hub offersgood fatigue strength in a medium-temperature environment.

The method of the invention imparts good adhesion between the compositeblades and the compacted metal. It enables the wheel to withstand highspeeds of rotation of about 1,000 revolutions per second, and hightemperatures.

Advantageously, the rim-forming closed cylindrical ring is made ofmetal, but it may also be made of a ceramic or composite material.

The orifices, which correspond to the predetermined cross-sectionalshape of the blades, may be cut in a preformed cylindrical ring.

However, to form a closed cylindrical ring, orifices that correspond tosaid predetermined cross-sectional shape of the blades may be initiallycut in a flat metal strip of predetermined width corresponding to thewidth of the hub of the wheel, and the metal strip provided with theorifices is then shaped into a closed cylindrical ring.

In a particular implementation, after making the assembly constituted bythe blades, by the metal or composite cylindrical ring, and by theannular rigid metal wire, the blade bases are soldered to the metal orcomposite cylindrical ring, and the sealed housing is connected to themetal or composite cylindrical ring, with only the blade bases and therigid metal wire being disposed inside the sealed housing in which thehot isostatic compaction operation is performed.

In which case, each of the blade bases (and the cylindrical ring if itis made of a composite) is advantageously covered with a layer ofsealant and/or with a diffusion barrier layer before the solderingoperation is performed.

In another particular implementation, the hot isostatic compaction isperformed in a sealed housing which surrounds the entire assemblyconstituted by the blades, by the cylindrical ring, by the rigid metalwire, and by the spacers or inserts.

This implementation is particularly simple because it does not involveany soldering around the blades, and poses no sealing problem. Metal orceramic spacer-forming inserts must merely be held between the bladesoutside the cylindrical ring so as to prevent the blades from beingcrushed, since the pressure is taken up by the inserts.

Advantageously, the hot isostatic compaction is performed at atemperature of about 1,000° C. and under a pressure of about 1,000 bars.These conditions depend on the material used for manufacturing the hub.

Regardless of the implementation, the metal alloy in powder form usedfor the hot isostatic compaction is advantageously of the same type asthe material forming the rigid metal wire. This makes the hub veryhomogeneous. However, different materials may also be chosen dependingon the applications for which the turbine wheel is to be used.

To enable the blade bases to be threaded onto the annular rigid metalwire, the opening therein is slightly wider than the depth of a holeformed in a blade base.

In the final position, one of the ends of the annular rigid metal wiremay be situated substantially half-way into the hole formed in a bladebase. In a variant implementation, in the final position, the two endsof the annular rigid metal wire are situated between two blades and saidtwo ends are clipped together.

Advantageously, a specific protective layer is deposited on each bladehead over the portion that projects from the cylindrical ring, so as toprovide the projecting portion of the blade head with protection againstoxidation and attack from aggressive media.

The invention also provides a one-piece turbine wheel of heterogeneouscomposition, the turbine wheel having blades made of a ceramic orcomposite material and inserted into a metal hub, the turbine wheelbeing applicable, in particular, to the field of aeronautical or spaceengineering, said turbine wheel being characterized in that each of theblades has an essentially right cylindrical shape with a cross-sectiondefining a predetermined non-circular shape, and includes a blade baseembedded in the metal hub and provided with a hole that extendsessentially perpendicular to the axis of the blade, a metal memberembedded in the hub passing through the holes in the various bladebases.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention will appear fromthe following description of particular implementations given by way ofnon-limiting example and with reference to the accompanying drawings, inwhich:

FIG. 1 is a perspective view of a portion of an example of a turbinewheel of the invention;

FIG. 2 is a perspective view of an example of a blade that is made of acomposite material and that may be incorporated into a turbine wheel ofthe invention;

FIG. 3 is a view of a portion of flat metal strip provided with openingsthrough which blades can pass;

FIG. 4 is a perspective view of a flat metal strip provided withopenings, showing the strip after it has been shaped into a closedcylindrical ring;

FIG. 5 is an axial section view showing how a blade is installed throughan opening in the ring shown in FIG. 4, and how a rigid wire is engagedfor retaining the base of the blade;

FIG. 6 is a plan view showing how the blades are engaged into the FIG. 4ring, and how the blade bases are threaded onto an open annular rigidwire;

FIGS. 7A and 7B show a possible example of the last two steps ofthreading blade bases onto an open annular rigid wire;

FIG. 8 is a perspective view of an assembly of the invention comprisingblades made of a composite material, inserted into a cylindrical ring,and having bases that are threaded onto a metal retaining wire;

FIG. 9 is a radial section view of the assembly shown in FIG. 8 placedin a housing so that a hot isostatic compaction can be performed;

FIG. 10 is a detail view in radial section showing how a blade issoldered to a cylindrical ring;

FIG. 11 is a detail perspective view in axial half-section showing ablade enclosed in a housing for the purposes of making the hub by hotisostatic compaction;

FIG. 11A is a detail view showing an example of how the two portions ofthe housing shown in FIG. 11 may be coupled together;

FIGS. 12 and 13 are perspective views showing two opposite faces of aturbine wheel of the invention provided with a metal housing for thepurposes of making the hub by hot isostatic compaction, with the endportions of the blades projecting from the housing; and

FIGS. 14 and 15 are axial section views showing two portions of ahousing for containing an assembly of the invention such as the assemblyshown in FIG. 8, the housing enabling a hub to be made by hot isostaticcompaction, with the entire blades being enclosed in the housing.

DETAILED DESCRIPTION OF PARTICULAR IMPLEMENTATIONS OF THE INVENTION

The method of the invention facilitates making a one-piece turbine wheelof heterogeneous composition, essentially comprising blades 16 made of acomposite material having a composite matrix, the blades being insertedinto a metal hub 40 made by powder metallurgy.

For example, the blades made of a composite material may be made ofcarbon-carbon or of carbon-silicon carbide.

Each of the blade heads 17 constituted by the portions of the bladesthat project from the hub 40 may be covered with a specific protectivelayer 171 for providing protection against oxidation and attack fromaggressive media (e.g. such as hydrogen or rocket propellantcomponents). The protective layer 171 may also play a part in sealingthe composite material.

Each of the blade bases 18 embedded in the hub 40 may also bepre-covered with a layer of sealant, or with a diffusion barrier layer180.

The hub 40 may be made from an alloy, e.g. based on nickel, titanium, oriron. However, it is easy to adapt the manufacturing method to a widevariety of types of alloy.

Such protective layers 171, diffusion barrier layers 171, or sealinglayers on the blades 16 may have thicknesses lying in the range a fewhundreds of a millimeter to a few millimeters, and they may be made byusing various techniques, e.g. such as plasma deposition, electrolyticdeposition, chemical vapor deposition or physical vapor deposition, anddeposition by painting.

The sealing or diffusion-barrier layers 180 deposited on the blade bases18 may also contribute to improving the interface between the metal ofthe hub and the composite material of the blade, and, in particular,they may have intermediate chemical compositions taking into account thedifferences in expansion behavior of the two materials constituting theblades 16 and the hub 40. By way of example, a sealing ordiffusion-barrier layer 180 may comprise an alloy based on copper andnickel.

In accordance with a major characteristic of the present invention, theblades 16 are essentially right-cylindrical with cross-sections that areof predetermined non-circular shapes.

FIGS. 1 and 2 show blades 16 having crescent-shaped cross-sections. InFIGS. 8, 9, 12, and 13, the blades 16 have rectangular cross-sections,so that they are in the shape of very simple rectangular blocks.

Various other cross-sectional shapes are possible, as a function of theapplications for which the turbine wheel is to be used.

Although the blades may be shaped individually, it is also possible,given their cylindrical shape, to make large numbers of themsimultaneously from a single cylindrical bar which has the desiredshape, and which is then merely cut up into lengths, each of whichcorresponds to a respective blade. This "sausage-making" technique ismade possible by the fact that the blade bases do not need to bedovetail or Christmas tree shaped as they do in existing turbine wheels,and the shape of the blade may be obtained by merely stacking up fibers.

In accordance with the invention, it is merely necessary to provide ahole 19 in each blade base 18, the hole extending perpendicular to thelongitudinal direction of the blade 16, so as to make it possible toinsert a rigid metal wire 30 (FIG. 1) which enables the various blades16 to be installed and to be retained while the hub 40 is being formed,as explained below. This type of installation technique avoids havingcomplicated shapes for the blade bases 18, while also increasing themechanical strength of the assembly.

In addition to manufacturing the blades 16, a metal or composite flatring 20 is manufactured to delimit the rim of the turbine wheel fromwhich the blades 16 inserted in the hub 40 are to project.

To this end, a flat metal strip 20 may be used in which a series ofregularly spaced-apart openings 21 are cut, each opening having the samecross-sectional shape as the blades 16 (FIG. 3). The openings may be cutby using various methods, e.g. such as punching, electro-erosion, lasercutting or water-jet cutting, or conventional machining.

Lengths of flat metal strip provided with openings 21 are then shapedinto rings 20 and the two ends of each length of strip shaped into aring are secured together in a region 22 (FIG. 4), e.g. by welding.

In a variant implementation, lengths of flat metal strip are initiallycut and shaped into closed rings 20, and openings 21 are then cut in theclosed cylindrical rings 20.

Each cylindrical ring 20 may also be made of a composite material, witha series of regularly spaced-apart openings 21 being provided in thering, e.g. by means of any one of the above-mentioned methods.

After the blades 16 and a closed cylindrical ring 20 provided withopenings 21 have been made, the ring 20 is disposed in an installationmember 210 (FIG. 5), e.g. comprising a cylindrical central core 211 anda cylindrical outer ring 212 that is coaxial with the core 211 and thatis connected thereto via a disk-shaped external cheek 213. The closedcylindrical ring 20 is inserted inside the outer cylindrical ring 212which holds it in position. The blades 16 are successively insertedthrough the holes 21 in the closed cylindrical ring 20 and they arepositioned against the central core 211 which serves as a centeringabutment for the blade bases 18.

As each new blade 16 is inserted into the rim-forming cylindrical ring20, an open annular rigid metal wire 30 which is preferably circular incross-section is inserted through the hole 19 in the blade 16.

In this way, the bases 18 of the blades 16 are threaded successivelyonto the annular metal wire 30 which has a smaller diameter than thecylindrical ring 20, and which is to be embedded in the hub 40 of theturbine wheel. The gap in the metal wire 30, which is toroidal or ofsquare cross-section, is slightly wider than the thickness of a bladebase 18, so that it is possible to engage a blade base 18 between thetwo free ends 31 and 32 of the rigid wire 30 (FIG. 6).

The wire 30 may be passed through the holes 19 in the blade bases 18 bymeans of a mechanism 220 placed on the other side of the wire from theinstallation support 210, the mechanism being centered by means of a pin240 on the central core 211, and including a clamp 230 that can beengaged in a groove 34 formed in the vicinity of a first free end 31 ofthe metal wire 30.

FIGS. 7A and 7B show an example of how the wire 30 may be threadedthrough the hole 19 in the last blade 16 to be installed, at the end ofthe threading process. A cylindrical insert 33 having the same diameteras the wire 30 is inserted into the hole 19 in the blade 16, and theblade 16 is positioned such that the hole 19 is situated between thefree ends 31 and 32 of the wire 30 (FIG. 7A). By rotating the wire 30,one free end 32 is inserted halfway into the hole 19, so that it pushesthe insert 33 into an offset position, thereby retaining the blade 16(FIG. 7B).

In a variant implementation, at the end of the process of threading theblades 16 onto the wire 30, both of the free ends 31 and 32 of the wire30 are situated between two blades 16, and they are clipped together.

FIG. 8 shows an example of the assembly as obtained at the end of thestep during which the blades 16 are inserted through the cylindricalouter ring 20, and the blade bases 18 are threaded onto the annularrigid wire 30. The FIG. 8 example shows fifteen rectangular-block shapedradial blades 16 regularly spaced apart over the cylindrical outer ring20 delimiting the rim of the turbine wheel. The inner metal wire 30retains the blade bases 18 that are to be embedded in the metal hub.Naturally, the number of blades 16 may differ from fifteen as a functionof the applications and of the dimensions of the turbine wheel.

The assembly shown in FIG. 8 constitutes the framework of the turbinewheel, and said assembly must then be inserted into a sealed housing soas to enable a metal hub to be made by powder metallurgy.

There are several different possible ways of making the hub.

In a first possible implementation shown in FIGS. 10, 12, and 13, theblades 16 are soldered to the outer ring 20 at the openings 21 by meansof a solder wire 22, so as to provide sealing between the blades 16 andthe ring 20. The blade bases 18 are themselves pre-sealed, or else theyreceive a layer 180 acting as a diffusion barrier, before they areinstalled, as indicated above. Each of the holes 19 that receive themetal wire 30 is also provided with a sealing layer 190 or a bushingbefore the blades are installed.

Once the blades 16 have been soldered to the composite or metalcylindrical outer ring 20, said ring may constitute the side wall of thehousing serving to make the hub by powder metallurgy. In which case, theonly elements of the housing that need to be added to the assembly shownin FIG. 8 to constitute a sealed enclosure are the metal front end face62 (FIG. 13) and the metal rear end face 61 (FIG. 12) which close offthe central hub portion delimited by the outer ring 20. As shown inFIGS. 12 and 13, metal or composite spacer-forming inserts 50 may bedisposed temporarily between the heads 18 of the blades 16 so as tolimit the stresses to which the blades 16 may be submitted during thehot isostatic compaction operation. In which case, one of the portionsof the housing, such as the rear face 61, may extend radially beyond theouter ring 20 so as to hold the inserts 50 which nevertheless remainoutside the housing in this implementation.

After a metal alloy in powder form 41 has been inserted into the sealedhousing, hot isostatic compaction is performed, e.g. at 1,000° C. andunder about 1,000 bars.

The inserts 50 are then removed, and the housing 61, 62 is machined soas to give the hub of the turbine wheel 100 its final shape. The blades16 then require only minor final adjustments while the turbine wheel isbeing balanced.

Another possible way of manufacturing the hub by powder metallurgy isdescribed below with reference to FIGS. 9, 11, 11A, 14, and 15.

In this particular implementation, it is not necessary to provide asealed bond between the outer ring 20 and each of the blades 16.However, an insert 50, e.g. made of metal or ceramic, must be disposedin each of the gaps between the blades 16, the inserts 50 extendingsubstantially over the entire height of the blade heads 17 projectingfrom the outer ring 20 (FIG. 9) so as to prevent the blades from beingcrushed under the action of the high pressures used. The inserts 50 maybe coated, e.g. with boron nitride so as to prevent them from adheringto the blades 16 made of a composite material, or to the outer ring 20,and so that they can be removed more easily after the hot isostaticcompaction operation.

In this implementation, the entire assembly as shown in FIG. 8, to whichthe inserts 50 have been added, as shown in FIG. 9, is incorporated in asealed housing 161, 162. No particular sealing needs to be provided atthe individual blades 16, and this simplifies the implementation. Thehousing 161, 162 may be formed by a back 161 (FIG. 14) and by a cover162 (FIG. 15).

The central portions 163 and 167 of the back 161 and of the cover 162define the end faces of the housing, and said central portions delimit avolume corresponding to the hub proper, i.e. to the space inside theouter ring 20. The peripheral portions 165 and 168 of the back 161 andof the cover 162 delimit a narrower space which corresponds to the widthof each of the heads 18 of the blades 16.

In FIGS. 11 and 15, reference 170 designates the channel via which themetal alloy in powder form 41 is inserted into the housing.

The two portions 161 and 162 of the housing are connected together insealed manner by welding, e.g. at a peripheral groove 166 formed in theback 161 and in which a lip 169 on the cover 162 (FIG. 11A) is engaged.

After the metal alloy in powder form 41 has undergone hot densificationinside the housing 161, 162 so as to form the metal hub, the housing161, 162 is removed by machining, the inserts 50 are removed from theempty spaces between the blade heads 18, and final machining isperformed on the turbine wheel so as to balance it.

The toroidal metal wire 30 is embedded in the metal hub at the end ofthe hot isostatic compaction operation, and it contributes not only toholding the blades in position during the hot isostatic compactionstage, but also to imparting greater tear-off strength to the blades sothat they can withstand greater centrifugal forces. The metal wire 30 isadvantageously made of the same material as the hot isostatic compactionmaterial, so as to make the hub more homogeneous, but this is notabsolutely necessary.

The method of the invention enables a one-piece turbine wheel orcompressor wheel 100 of heterogeneous composition to be made simply, inwhich the blades 16 made of a ceramic or composite material and insertedinto the metal hub 40 may have very simple shapes and may be moreeffectively secured to the metal hub 40. In the finished product, eachof the bodies of the blades 16 constituted by blade heads 17 projectingfrom the hub 40, and by blade bases 18 embedded in the metal hub, has anessentially right cylindrical shape with a cross-section ofpredetermined non-circular shape. Once embedded in the hub 40, the metalwire 30 continues to pass through the holes 19 formed in the blade bases18, each hole extending essentially perpendicular to the axis of therespective blade 16.

I claim:
 1. A method of manufacturing a turbine wheel having blades madeof a ceramic or composite material and inserted into a metal hub, saidmethod being characterized in that it comprises the following steps:theblades are manufactured from a ceramic or composite material, each bladehaving an essentially right cylindrical shape defining an axis with across-section defining a predetermined non-circular shape, and a hole isformed in the base of each blade, the hole being essentiallyperpendicular to the axis of the blade; a closed rim forming cylindricalring is formed of predetermined height that corresponds to a width ofthe hub of the turbine wheel, the ring being provided with orificescorresponding to the predetermined cross-sectional shape of the blades;the bases of the blades are inserted through said orifices in therim-forming cylindrical ring; the bases of the various blades insertedthrough the cylindrical ring are successively threaded onto an openannular rigid metal wire which has a smaller diameter than thecylindrical ring and which passes through said holes formed in the basesof the blades; removable spacers or inserts are interposed between headsof the blades projecting radially outwards beyond said cylindrical ring;an assembly constituted by at least the bases of the blades, by thecylindrical ring and by the annular rigid metal wire is disposed insidea sealed housing have been interposed between heads of the bladesprojecting radially outwards beyond said cylindrical ring; hot isostaticcompaction is performed so as to compact a metal alloy in powder formthat is inserted into the sealed housing so as to make the hub of theturbine wheel while embedding the blade bases and the annular rigidmetal wire by using powder metallurgy technique; and an outside portionof the sealed housing delimiting the hub of the turbine wheel ismachined and said removable spacers are removed.
 2. A method accordingto claim 1, characterized in that a long cylindrical length of ceramicor composite material is manufactured in a single operation, said lengthhaving a cross-section of predetermined uniform shape, and then saidlong length of ceramic or composite material is cut up into individualblades.
 3. A method according to claim 1, characterized in that saidcylindrical ring is formed of metal.
 4. A method according to claim 1,characterized in that said cylindrical ring is formed of a compositematerial.
 5. A method according to claim 1, characterized in that saidorifices, which correspond to the predetermined cross-sectional shape ofthe blades, are cut in a pre-formed cylindrical ring.
 6. A methodaccording to claim 3, characterized in that, to form the closedcylindrical ring, orifices that correspond to said predeterminedcross-sectional shape of the blades are initially cut in a flat metalstrip of predetermined width corresponding to the width of the hub ofthe wheel, and the metal strip provided with the orifices is then shapedinto said closed cylindrical ring.
 7. A method according to claim 1,characterized in that, after making the assembly constituted by theblades, by the cylindrical ring, and by the annular rigid metal wire,the blade bases are soldered to the cylindrical ring, and the sealedhousing is connected to the cylindrical ring, with only the blade basesand the rigid metal wire being disposed inside the sealed housing inwhich the hot isostatic compaction operation is performed.
 8. A methodaccording to claim 7, characterized in that each of the blade bases iscovered with a layer of sealant or with a diffusion barrier layer beforethe soldering operation is performed.
 9. A method according to claim 1,characterized in that the hot isostatic compaction is performed in thesealed housing which surrounds the entire assembly constituted by theblades, by the cylindrical ring, by the rigid metal wire and by thespacers.
 10. A method according to claim 1, characterized in that thehot isostatic compaction is performed at a temperature of about 1,000°C. and under a pressure of about 1,000 bars.
 11. A method according toclaim 1, characterized in that the blades are made of compositematerials of the carbon-carbon type or of the carbon-silicon carbidetype.
 12. A method according to claim 1, characterized in that the metalalloy in powder form used for the hot isostatic compaction is of thesame type as the material of the annular rigid metal wire.
 13. A methodaccording to claim 1, characterized in that the opening in the annularrigid metal wire is slightly wider than the depth of a hole formed inthe blade base.
 14. A method according to claim 13, characterized inthat, in the final position, one of the ends of the annular rigid metalwire is situated substantially half-way into the hole formed in theblade base.
 15. A method according to claim 13, characterized in that,in the final position, the two ends of the annular rigid metal wire aresituated between two blades.
 16. A method according to claim 1,characterized in that the metal alloy in powder form compacted duringthe hot isostatic compaction is based on nickel, titanium or iron.
 17. Amethod according to claim 1, characterized in that the sealed housing isformed of a back-forming first metal part and of a cover-forming secondmetal part, the two parts being welded together, and in that the hotisostatic compaction is performed via one of said first and second metalparts.
 18. A method according to claim 1, characterized in that aspecific protective layer is deposited on each blade head over theportion that projects from the cylindrical ring, so as to provide theprojecting portion of the blade head with protection against oxidationand attack from aggressive media.
 19. A one-piece turbine wheel ofheterogeneous composition, the turbine wheel having blades made of aceramic or composite material and inserted into a metal hub, saidturbine wheel being characterized in that each of the blades has anessentially right cylindrical shape with a cross-section defining apredetermined non-circular shape, and includes a blade base embedded inthe metal hub and provided with a hole that extends essentiallyperpendicular to the axis of the blade, a metal member embedded in thehub passing through the holes in the various the blade bases, the bladebases, the metal member, and the metal hub being integrally formed byhot isostatic compaction.
 20. A turbine wheel according to claim 19, asused in the field of aeronautical or space engineering.
 21. The methodaccording to claim 1, including manufacturing a long ceramic orcomposite material in a single operation, said length having across-section of predetermined uniform shape, and then cutting up saidlong length of ceramic or composite material into individual blades;whereinsaid cylindrical ring is formed of a metal or of a compositematerial; said orifices, which correspond to the predeterminedcross-sectional shape of the blades, are cut in said pre-formedcylindrical ring; the hot isostatic compaction is performed in thesealed housing which surrounds the entire assembly constituted by theblades, by the cylindrical ring, by the rigid metal wire and by thespacers; the hot isostatic compaction is performed at a temperature ofabout 1,000° C. and under a pressure of about 1,000 bars; the blades aremade of composite materials of the carbon-carbon type or of thecarbon-silicon carbide type; the metal alloy in powder form used for thehot isostatic compaction is of the same type as the material of theannular rigid metal wire; the opening in the annular rigid annular wireis slightly wider than the depth of the hole formed in a blade base; inthe final position, one of the ends of the annular rigid metal wire issituated substantially half-way into the hole formed in a blade base andthe two ends of the annular rigid metal wire are situated between twoblades; the metal alloy in powder form compacted during the hotisostatic compaction is based on nickel, titanium or iron; the sealedhousing is formed of a back-forming first metal part and of acover-forming second metal part, the two parts being welded together,and the hot isostatic compaction is performed via one of said first andsecond metal parts; and a specific protective layer is deposited on eachblade head over the portion that projects from the cylindrical ring, soas to provide the projecting portion of the blade head with protectionagainst oxidation and attack from aggressive media.